The field of psychoacoustics refers to the study of the perception of sound. This includes how humans listen, their physiological responses, and the physiological impact of music and sound on the human nervous system. In particular, for the development of modern communication systems the knowledge how acoustic stimuli are processed by the auditory system is important in the development of new digital audio technologies and in the improvement of existing technologies. Audio codecs, which are essential components in multimedia and broadcast services depend on the knowledge of the characteristics of the human auditory system to compress audio information for efficient transmission and storage at low bit rates. In addition, objective schemes for quality measurement, which also depend heavily on psychoacoustic knowledge, have been developed to simulate subjective ratings of audio quality.
Almost all modern audio codecs [1-5] exploit the concept of encoding and transmitting only part of the signal frequency components of an audio signal, and reconstructing the remaining frequencies of the audio signal at the decoder. Typically, only the low frequency bands (LB) of a signal are transmitted, and the high frequency bands (HB) of the signal are subsequently reconstructed by means of so-called bandwidth extension (BWE). In a typical BWE scheme, the frequency content of a signal is extended by translating or flipping the available frequency components from a neighbouring band (usually the available LB). However, a signal reconstructed in such a manner does not have a HB that match exactly the HB of the original audio signal, due to certain artifacts that can be perceived in the reconstructed signal. To minimize the impact of these artifacts, in a BWE scheme, the gain of reconstructed HB is typically kept below the original HB gain, which leads to a reconstructed signal with modified psychoacoustic properties. Among the most affected properties are the sensation of loudness, and sensation of sharpness. Loudness is related to the signal intensity or sound pressure of the speech signal. Sharpness is related to the energy distribution over frequency of the speech signal and increase with the relative increase of high-frequency components. When the signal is band-limited or a conventional BWE scheme is applied, both the perceived loudness and sharpness of the reconstructed signal decrease in comparison to the original signal, which leads to drop in subjective quality.
Therefore there is a need for methods and arrangements enabling improving the perceived loudness and sharpness of a received/decoded signal.